This invention relates to a disazo compound, method for preparing the same, and electrophotographic element containing the same for use in electrophotography. More particularly, this invention relates to an electrophotographic element having a photosensitive layer containing a disazo compound as a charge generating substance which generates a charge carrier by light irradiation.
Heretofore, there were used inorganic photosensitive materials such as selenium, selenium alloy, cadmium sulfide, zinc oxide and the like. Among them, selenium type photosensitive material was widely used because it has generally superior properties in respect to receiving potential, dark decay, sensitivity and the like. However, the selenium type electrophotographic element has such disadvantages as that the control of properties is difficult since it is prepared by vapor deposition; that the manufacturing cost is high; that it is difficult to work the element into a belt-like product due to lack of flexibility; and that the handling of the element is not easy because it is too sensitive to mechanical impact and heat.
There was also used an element having a photosensitive layer containing an organic photosensitive material superior in flexibility and easy in production, for example, a charge transfer comples of 2,4,7-trinitro-9-fluorenone and poly-N-vinylcarbazole. However, the sensitivity of this element was too low and therefore unsuitable as an electrophotographic element for a high speed copying machine.
Recently, various studies have been carried out to remove disadvantages for these electrophotographic elements. Among them, there is noted a separate function type electrophotographic element wherein the generation of a charge carrier and the transfer of the generated charge carrier are respectively conducted by separate substances. As the separate function type electrophotographic element, there are enumerated a laminated type electrophotographic element having a photosensitive layer prepared by laminating a charge generating layer containing a charge generating substance to generate a charge carrier by light irradiation and a charge transfer layer containing a charge transfer substance to transfer the generated charge, a dispersed type electrophotographic element prepared by dispersing a charge generating substance in a charge transfer medium containing a charge transfer substance, and the like. Since these photosensitive materials are widely selected and it is possible to enhance the sensitivity, they are noted as an electrophotographic element for a plain paper copier.
Examples of these electrophotographic elements include:
(1) a laminated type electrophotographic element using a thin layer formed by vapor depositing perillene derivatives as a charge generating layer and oxadiazole derivatives as a charge transfer layer (U.S. Pat. No. 3,871,882); PA1 (2) a laminated type electrophotographic element using a thin layer formed by coating an organic amine solution of Chloro Dian Blue as a charge generating layer and hydrazone compound as a charge transfer layer (Japanese Patent Publication No. 55-42380); and the like. PA1 Y.sub.1 : hydrogen, halogen, substituted or non-substituted alkyl group, substituted or non-substituted alkoxy group, carboxyl group, sulfo group, substituted or non-substituted sulfamoyl group or ##STR10## (wherein R.sub.4 represents hydrogen, alkyl group or its substituted compound, phenyl group or its substituted compound, and Y.sub.2 represents cyclic hydrocarbon or its substituted compound, heterocycle or its substituted compound, or ##STR11## wherein R.sub.5 represents a cyclic hydrocarbon or its substituted compound, heterocycle or its substituted compound, or styryl group or its substituted compound, and R.sub.6 represents hydrogen, alkyl group, phenyl group or their substituted compound, or R.sub.5 and R.sub.6 may form a ring with carbons bonded thereto); PA1 Z: cyclic hydrocarbon or its substituted compound, or heterocycle or its substituted compound; PA1 n: an integer of 1 or 2; PA1 m: an integer of 1 or 2. ##STR12## wherein R.sub.7 in the above formula (X) and (XI) represents a substituted or non-substituted hydrocarbonyl group, and X.sub.1 is the same as mentioned above; ##STR13## wherein R.sub.8 represents an alkyl group, carbamoyl group, carboxyl group or its ester, and Ar.sub.1 represents a cyclic hydrocarbon or its substituted compound, and X.sub.1 is the same as mentioned above; ##STR14## wherein R.sub.9 in the above formula (XIII) and (XIV) represents hydrogen or substituted or non-substituted hydrocarbonyl group, and Ar.sub.2 represents cyclic hydrocarbon or its substituted compound.
However, these conventional laminated type electrographic elements have not only advantages but also various disadvantages. For example, the above electrophotographic element (1) using perillene derivatives and oxadiazole derivatives has a disadvantage that the manufacturing cost is very high because of forming a charge generating layer by vapor deposition. The above electrophotographic element (2) using Chloro Dian Blue and hydrazone compound must use an organic amine (for example, ethylene diamine) as a coating solvent for forming a charge generating layer, which is difficult in handling.
As a photosensitive material having a good sensitivity which can be easily manufactured, there are enumerated a photosensitive material using a disazo pigment having styrylstilbene structure as a charge generating substance (Japanese Laid Open No. 53-133445); a photosensitive material using a disazo pigment having dibenzothiophene structure as a charge generating substance (Japanese Laid Open No. 54-21728); a photosensitive material using a disazo pigment having carbazole structure (Japanese Laid Open Nos. 53-95033 and 53-95966); a photosensitive material using a trisazo pigment having triphenyl amine structure (Japanese Laid Open No. 53-132347); a photosensitive material using a disazo pigment having oxazole structure (Japanese Laid Open No. 54-12742); a photosensitive material using a disazo pigment having disstyrylcarbazole structure (Japanese Laid Open No. 54-14967); a photosensitive material using a disazo pigment having bisstilbene structure (Japanese Laid Open No. 54-17733); a photosensitive material using a disazo pigment having fluorenone structure (Japanese Laid Open No. 54-22834); and the like. However, these conventional photosensitizers also have merits and demerits, and a development of new photosensitive materials having better properties is desired.